中文摘要：

对LY12CZ铝合金薄壁圆管试样进行多种路径下按高一低和低一高顺序作用的两级变幅载荷下的疲劳损伤累积实验。分析两级变幅循环载荷下各种路径的疲劳累积损伤规律，以及第一级载荷作用循环次数对试件总的疲劳寿命的影响。实验结果表明，在多轴拉扭复合加载的情况下，累积损伤规律呈现出非线性，且损伤程度受第一级载荷作用循环次数影响。

英文摘要：

Experiments on fatigue cumulative damage of LY12CZ aluminum alloy thin-walled tubular specimens are conducted under high-low and low-high two-level cyclic loading. The fatigue damage cumulative rules under two-level cyclic loading of different loading modes are analyzed, and the effect of the cycle number for the first level loading on the fatigue life of the specimen is also considered. Experiments showed that, the fatigue cumulative damage is nonlinear under muhiaxial combined tension-torsion loading, and the number of the cycles for the first level loading affects the total fatigue life.